You currently have javascript disabled. Several functions may not work. Please re-enable javascript to access full functionality.

Welcome to the FMCA Motorhome Forums!

Create a sign-in account to gain access to all of our features. Once registered and signed in, you can create topics; post replies to existing topics; upload pictures; manage your profile; get your own private messenger; create blogs; and more. Sign up now! Already have an account? Sign in.

NEW USERS: For your login to carry over to the Forums, you must first sign in on the FMCA.com main site, log out, and then sign in again.

New hydraulic pump (made my fan ran per specs), new steel radiator, new radiator hoses, new thermostat. Water pump fine. Ditto fanbelts. Weight is 36, 000 for coach and 6000 lbs for toad for about 42, 000 total (per CAT scale) Coach is 2006 County Coach, tag and rated to 52, 000 lbs, side radiator. The engine was new about 12, 000 miles ago and had the same problem with old engine.

I have driven at 1800 rpms, 1400 rpms with and without cruise control, downshifted to 4th etc.

Engine overheat per Slverleaf to 226 and then derates and if I continue to drive, will shutdown. Does this on grades. Does find on flats. So any ideas, etc

We have a 400 ISL. Our coach GVWR is 37,600 and the GCWR is 47,600. Our last weighing we came in with a GCW of 37,925. We have never had any problem with overheating. You are about 4000 pounds heavier or about 10% over our weight. I wouldn't think that little difference would make the engine overheat. We top out in the low to mid 190's on a long grade on a 90+ degree day. Since you had the same problem with the previous engine, has this been a problem since the coach was new? Perhaps the problem lies outside the engine.

After 9 1/2 years full time in our motor home and being Winter Texans we are now living at Sandpipers Resort in Edinburg, Texas. Now we are Summer Chickens!

"The tipi is much better to live in; always clean and warm in winter, cool in summer, easy to move... If the Great Spirit wanted men to live in one place he would have made the world stand still." -- Flying Hawk, South Dakota Oglala Sioux

Have you verified that the fans ARE going to high-speed. Check, but on many, disconnecting the hydraulic fan controller wire defaults the fan speed to high. If it doesn't overheat with wire disconnected (again verify this is how yours is set up) suspect controller issue OR improper input to controller from engine computer.

My 400 ISL did the same thing. Turns out problem was clogged radiator (road debris) on engine side of rear mounted radiator. Cleaned it and now pulls grades without going over 195 or so. If your rad has been replaced, obviously not your problem, but might help someone else with similar issue.

Just wondering what you intake manifold temps run when you water temps hit 226 deg.

The only time we had major cooling issues was when the thermostat failed, driving at any altitude or temperatures was impossible with the slightest grade.

When its hot (90+) and running at over 5000 ft. I'm right at the point where my temps. start to go above the comfort zone.

The rest of the time everything runs within or near nominal.

Same elevation, same road: early AM or evening when its just a little cooler, back around 80 deg. the engine coolant runs right at 190/195 and the intake temp only runs around 170 / 180 when running up hill.

I do pressure wash after returning from a trip of over 3K when we return home and more often should we travel in dusty areas when a truck stops shows. up.

I'm thinking that the CAC and radiator cooling capacity is maxed out around 90deg. and over 5000ft. pulling a grade for an extended period.

I am at sea level to about 1000 feet when I am testing. The road is the Alamont grade, I580 eastbound toward Livermore, ca. I have ran with trans doing the work and with me controlling the RPM and mph.

The sensors check OK, next step is fan controller and fan motor. The radiator is brand new, steel and copper, ditto the thermostat.

No one has mentioned this yet but the engine is supplied to the manufacturer and then the manufacturer decides what radiator to put with the engine. The size of the radiator and the kind of fan, the fan shrouding, radiator grille opening size, etc. are all determined by the manufacturer. I have heard of cases where radiator size varies for the same engine, some manufacturers going for a larger radiator than others. I don't know what the size of our radiator is, don't know how to measure except for square inches of open space on the radiator. I measure ours at about 24 x 48 inches, about 1152 square inches. I wonder if we are all talking about the same size radiator (measure the finned area only).

After 9 1/2 years full time in our motor home and being Winter Texans we are now living at Sandpipers Resort in Edinburg, Texas. Now we are Summer Chickens!

"The tipi is much better to live in; always clean and warm in winter, cool in summer, easy to move... If the Great Spirit wanted men to live in one place he would have made the world stand still." -- Flying Hawk, South Dakota Oglala Sioux

Still working on the problem. With the cooler weather everything is working OK. Still seeing temps in the 216 range on steep hills. I am letting the Allison do the shifting and thinking for me. Seems to be keeping the engine between 1200 and 1600 rpms.

Cummins 400 ISL isn't a motor that I have worked on much, however here is a couple of thoughts. This unit is 100% electronic as such the computer will hold fault codes. If you have a mechanic that you use regularly they should be willing to flash your computer and pull any fault codes as a courtesy. The usual fee is $90 to $150 elsewhere.

I saw several others posting suggestions, I would like to offer the following;

Serpentine belt for slippage. ( Although a slipping belt is noisy and your charging system would show voltage drop ) While checking for slippage pay attention to the tensioner (yes that spring can be checked using a torque wrench )

Coolant system; double check proper level of coolant as well your radiator cap. If the seal on your cap won’t hold pressure that will increase temperature, while cooler weather allows for proper operation. Lastly you can pull the radiator and have a flow test preformed to check for decreased flow, there by decreasing the cooling properties, due to numerous reasons.

Proper Install as motor coaches are built on chassis provided by suppliers and then retro fitted by manufacture. They may have changed ( under sized hose or hoses or installed on tight binds resulting in decreased flow ) Under sized Radiator. If you had a larger alternator installed ( Neihoff or Leece Neville ) it’s possible that pulleys could have been changed this would effect the RPM of the water pump, resulting in decreased GPM flow.

It is possible that the transmission cooler could also be air flow restricting your radiator, have your mechanic check that as well.

I haven't reported back as the weather has been cold. Drove to Abq in Nov (some pretty steep grades on Hwy 58 east bound and I40 though Az andCa. No problems.

But I know with hot weather coming the problem will return. Having the mech do the checks that many of you suggested (thanks). Installing a new regulator and as a back up installing a manual switch so I can default the fan to high, if necessary.

I had the opportunity to compare my fan speed to another 2006 Allego that had the same engine, etc and his fan on high made mine sound like a baby fan, even I reported earlier, my fan speed has increased a lot and is pulling a lot of air. I would appreciate it, if the economy increases, that you think of me as I've tried to do my share. (Insert smiley face & empty wallet here)

Here's something to check if everything else has failed. If your rig has an exhaust retarder brake, and most diesel pushers do, make sure it's working correctly. If it does not *release* completely when the brake is off, you will have an exhaust restriction. This is bad when your engine needs to produce a lot of power, such as on a hill. Overheating is a sure bet, along with possible turbo damage.

I have an ISL set at 370hp. The thermostat is a 170 degree one - I thought it should be higher but my mechanic tells me this is correct for this engine.

Normal temps on flat ground runs very close to the 170 point. When I hit the hills (Bighorn Mountains) last August and let the Allison do it's thing the temps start to climb fast. Going up (eastbound US 14) is about 15 miles of 6-8% grade. Letting the Allison do it's thing let the RPM stay around 1500 (4th gear) resulting in the rapid rise in temp. By manually downshifting (3rd) to keep the RPM between 1800-2000 the engine stayed below 190. You have to keep air moving through the engine. Third gear provided more than enough speed due to very twisty roads with some 25-35 mph turns. Wouldn't want to go up much faster anyway.

Do you have an exhaust temperature (Pyrometer) on yours? By keeping the RPM up you will keep the exhaust temps down resulting in lower engine temperature.

Dean, not to butt in, but let me ask you this - you say your fan is blowing and it blows off your hat, but, just for grins, can you tell us if heat is actually exiting the engine compartment? Like most vehicles, and especially modern cars, trucks and industrial equipment, everything that's packed and crammed into the engine compartment is dependent upon cooling air entering and exiting. Is there an inlet/outlet that may be clogged? Does your diesel have a cold shroud in front of the radiator that isn't opened all the way? Just asking....